Atazanavir sulfate is known by the chemical name (3S,8S,9S,12S)-3,12-bis(1,1-dimethylethyl)-8-hydroxy-4,11-dioxo-9-(phenylmethyl)-6-[[4-(2-pyridinyl) phenyl]methyl]-2,5,6,10,13-pentaazatetradecanedioic acid dimethyl ester sulfate. Atazanavir sulfate is an antiviral agent and anti-HIV protease inhibitor. Atazanavir sulfate is represented by the following structure:

Atazanavir and its sulfate salt may be prepared using the procedures described in DE Patent No. 2007751, U.S. Pat. No. 3,663,607 and U.S. Pat. No. 3,836,671.
Polymorphism is defined as “the ability of a substance to exist as two or more crystalline phases that have different arrangement and/or conformations of the molecules in the crystal Lattice. Thus, in the strict sense, polymorphs are different crystalline forms of the same pure substance in which the molecules have different arrangements and/or different configurations of the molecules”. Different polymorphs may differ in their physical properties such as melting point, solubility, X-ray diffraction patterns, etc. Although those differences disappear once the compound is dissolved, they can appreciably influence pharmaceutically relevant properties of the solid form, such as handling properties, dissolution rate and stability. Such properties can significantly influence the processing, shelf life, and commercial acceptance of a polymorph. It is therefore important to investigate all solid forms of a drug, including all polymorphic forms, and to determine the stability, dissolution and flow properties of each polymorphic form. Polymorphic forms of a compound can be distinguished in the laboratory by analytical methods such as X-ray diffraction (XRD), Differential Scanning calorimetry (DSC) and Infrared spectrometry (IR).
Solvent medium and mode of crystallization play very important role in obtaining a crystalline form over the other.
Atazanavir sulfate can exist in different polymorphic form, which differ from each other in terms of stability, physical properties, spectral data and methods of preparation.
U.S. Pat. No. 6,087,383 described the preparation of atazanavir bisulfate in the form of Type-I crystals which appear to be an anhydrous/desolvated crystalline form and Type-II crystals which are a hydrated, hygroscopic crystalline form.
WO Patent Publication No. 2005/108349 disclosed two crystal forms, pattern C, form E3 of atazanavir bisulfate and also disclosed process for the preparation of atazanavir bisulfate form A (equivalent to Type 1 crystals obtained in Example 3 of U.S. Pat. No. 6,087,383). According to WO Patent Publication No. 2005/108349, pattern C crystals of atazanavir bisulfate was obtained by stirring a suspension of the form A crystals of atazanavir bisulfate in water.
We have discovered a stable novel crystalline form of atazanavir sulfate. The novel crystalline form is stable over the time and has good flow properties and so, the novel crystalline form is suitable for formulating atazanavir sulfate.
One object of the present invention is to provide a novel crystalline form of atazanavir sulfate and a process for preparing it.
According to another object of the present invention is to provide pharmaceutical compositions containing the novel crystalline form of atazanavir sulfate.